The present invention is related to end of injection pressure reduction and specifically to the operation of a check valve by controlling the flow rate into and out of a check control cavity.
Reducing emissions is a top priority for today""s engine manufacturers. As the government continues to tighten emission requirements, manufacturers must find new ways to reduce engine emissions while still providing powerful, economic engine operation. One area that engine manufacturers have focused on is fuel injection.
Fuel injection plays a crucial role in the amount of emissions created during combustion. Numerous fuel injection variables, including fuel pressure, spray pattern, droplet size, number of injections and injection timing impact emissions. In order to properly control these parameters, fuel injectors have become more complicated and more precise. For example, one exemplary design of a fuel injector is a hydraulically actuated electronically controlled unit injector such as a Caterpillar HEUI(copyright) B unit injector. This unit injector uses actuation fluid to pressurize fuel for injection. This allows tight control over how the fuel is pressurized and the timing of the pressurization. Further, a direct operated check is used to better control the exact timing of the injection. Specifically, the check can be closed when actuation fluid is present in the check control cavity, thereby hydraulically overcoming or at least balancing the check against pressurized fuel and preventing injection. Injection is achieved when fuel is pressurized and the check control cavity is vented, allowing the fuel pressure to overcome a check spring bias and push the check open.
As emissions regulations have increased, further injection developments have occurred. For example, it may be desirable to control and vary injection pressure both at the beginning and end of injection. However, even today""s advanced injectors may have difficulty controlling injection pressure at the beginning and the end of injection. For example, the hydraulically actuated electronically controlled unit injector briefly described above, can control the injection pressure at the beginning of the injection, allowing for a ramp rate shape but is designed to cut off injection almost immediately at the end of injection. Unfortunately, it has been shown that abruptly cutting off injection in this manner can cause unwanted emissions.
The present invention is intended to overcome one or more of the above problems.
In a first embodiment, a fuel injector comprises a nozzle tip defining a high pressure fuel cavity and an orifice connecting the high pressure fuel cavity to an outside to the nozzle tip. A check valve is at least partially disposed in the high pressure fuel cavity and moveable between a first position in which the orifice is in fluid communication with the high pressure fuel cavity and a second position in which the check blocks fluid communication of the orifice with the high pressure fuel cavity. The check has an opening hydraulic surface in said high pressure fuel cavity and a closing hydraulic surface in said check control cavity. The fuel injector also comprises a check control cavity, a first valve arrangement to selectively connect the check control cavity to a high pressure source or a low pressure drain, and a flow control valve in fluid communication with the check control cavity; the flow control valve having a first flow rate in a first direction and a second flow rate in a second direction.
In another embodiment, a method of operating a check with a check control cavity comprises venting the check control cavity at a first flow rate to allow injection and pressurizing the check control cavity at a second flow rate, different from the first flow rate to stop injection.
In another embodiment, a fuel injector comprises a nozzle tip defining a high pressure fuel cavity and an orifice connecting the high pressure fuel cavity to an outside to the nozzle tip. A check valve is at least partially disposed in the high pressure fuel cavity and moveable between a first position in which the orifice is in fluid communication with the high pressure fuel cavity and a second position in which the check blocks fluid communication of the orifice with the high pressure fuel cavity. The check has an opening hydraulic surface in said high pressure fuel cavity and a closing hydraulic surface in said check control cavity. The fuel injector also comprises a check control cavity, a first valve arrangement to selectively connect the check control cavity to a high pressure source or a low pressure drain, and means for controlling flow, the means being in fluid communication with the check control cavity and having a first flow rate in a first direction and a second flow rate in a second direction.